Motor Control Flashcards
What are the 2 broad principles of motor control and explain them?
Hierarchical organisation - higher order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity).
Functional segregation - Different areas that control particular aspects of movements.
The brainstem passes motor commands from the cortex to where?
Spinal cord
The motor cortex receives information from other cortical areas and sends commands to where?
Thalamus and brainstem
What structures adjust commands received from other parts of the motor control system?
Cerebellum and basal ganglia
Whats the difference between a pyramidal descending and extrapyramidal descending tract?
Pyramidal tracts pass through the pyramids of the medulla whereas extrapyramidal tract don’t.
List the major descending pyramidal tracts and the major descending extrapyramidal tracts.
Pyramidal:
Corticospinal + corticobulbar
Extrapyramidal: vestibulospinal, tectospinal, reticulospinal, rubrospinal
Where does the primary motor cortex reside?
Precentral gyrus anterior to the central sulcus.
What is the function of the primary motor cortex?
Controls fine, discrete, precise voluntary movements.
Provides descending signals to execute movements.
Where is the premotor cortex relative to the primary motor cortex?
Anterior to the primary motor cortex.
What is the function of the premotor area?
Concerned with movement planning and regulates externally cued movements (e.g. seeing an apple and reaching out for it).
Where is the supplementary motor area located relative to the primary motor cortex?
Located anterior and medial to the primary motor cortex.
What is the function of the supplementary motor area?
Involved in planning complex movements (internally cued, speech). Becomes active prior to voluntary movement.
What percentage of motor descending fibres of the corticospinal tract decussate at the medulla?
80-85% > form the lateral corticospinal tract > innervate the limb muscles
What does the anterior corticospinal tract supply motor innervation to?
Innervate the axial musculature (trunk muscles)
Explain the function of the corticobulbar tract.
The corticobulbar tract is responsible for providing voluntary movements for the face and neck.
UMNs synapse with brainstem cranial nuclei:
- Oculomotor, trochlear and abducens - Movements of the extra-ocular muscles
- Trigeminal - Muscles of mastication
- Facial - Muscles of the face
- Hypoglossal - Tongue
What is the function of the vestibulospinal tract?
Stabilise head during body movements, or as head moves.
Coordinates head movements with eye movements.
Mediates postural adjustments.
What is the function of the reticulospinal tract?
Changes in muscle tone associated with voluntary movement.
Postural stability.
What is the most primitive descending tract from the medulla and pons?
Reticulospinal
Where does the tectospinal tract arise from?
Superior colliculus of midbrain.
What is the function of the tectospinal tract?
Orientation of the head and neck during eye movements.
What is the origin of the rubrospinal tract?
From red nucleus of the midbrain.
What is the function of the rubrospinal tract?
Innervate LMNs of flexors of the upper limb.
(In humans this function is mainly taken over by the corticospinal tract. The rubrospinal tract only comes into play when there are lesions in the CNS).
List the negative signs a patient would present with if they had an UMN lesion.
Loss of voluntary motor function
Paresis - graded weakness of movements.
Paralysis (plegia) - complete loss of voluntary muscle activity.
List the positive signs a patient with an UMN lesion would present with.
Increased abnormal motor function due to loss of inhibitory descending inputs.
Spasticity - increased muscle tone
Hyper-reflexia - exaggerate reflexes.
Clonus - abnormal oscillatory muscle contraction.
Babinski’s sign
What is apraxia?
A disorder of skilled movement, patients are not paretic however have lost information regarding how to perform skilled movements.
Lesions or any disease to which areas of the cerebral cortex may lead to a patient developing apraxia?
Inferior parietal lobe, frontal lobe (premotor cortex, supplementary motor area -SMA)
What are the most common causes of apraxia?
Stroke and dementia
Where do LMN lesions occur?
Cranial nerve nuclei to corticobulbar tracts or within the spinal cord for innervating limb muscles.
List the symptoms a patient with a LMN may present with.
Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: Damaged motor units produce spontaneous action potentials, resulting in a visible twitch.
Fibrillations: Spontaneous twitching of individual muscle fibres; recorded during electromyography examination.
